Circuit protective device and method for manufacturing the same

Abstract

A circuit protecting element includes insulating substrate ( 11 ), a pair of surface electrodes ( 12 ) provided to both ends of a top face of insulating substrate ( 11 ), element ( 13 ) bridging the pair of surface electrodes ( 12 ) and electrically connected to the pair of surface electrodes ( 12 ), base layer ( 14 ) formed between element ( 13 ) and insulating substrate ( 11 ), and insulating layer ( 15 ) covering element ( 13 ). Base layer ( 14 ) is formed of a mixture of diatom earth and silicone resin. The structure discussed above allows stabilizing the blowout characteristics of the circuit protecting element.

The invention claimed is: 
     
       1. A circuit protecting element comprising:
 an insulating substrate; 
 a pair of surface electrodes formed on both ends of a top face of the insulating substrate; 
 a base layer disposed on the top face of the insulating substrate; 
 an element covering the base layer and bridging the pair of surface electrodes, and electrically connecting with the pair of surface electrodes; and 
 an insulating layer covering the element, 
 wherein the insulating layer is comprised of a first insulating layer, 
 wherein the element has a plurality of trimming grooves, 
 wherein the first insulating layer is in physical contact with the base layer via the trimming grooves, 
 wherein none of the trimming grooves reach the insulating substrate, 
 and wherein the element is prevented from bulging out from the base layer in a lateral direction. 
 
     
     
       2. The circuit protecting element of  claim 1 , wherein the base layer is formed of a mixture of diatom earth and silicone resin, and wherein the mixture of the diatom earth and the silicone resin contains the diatom earth in a range of 50-90 volumetric %. 
     
     
       3. The circuit protecting element of  claim 1 , wherein the base layer is formed of a mixture of diatom earth and silicone resin, and wherein the silicone resin of the base layer is colored. 
     
     
       4. The circuit protecting element of  claim 1 , wherein the base layer is formed of a mixture of diatom earth and silicone resin, wherein the insulating substrate contains alumina, and wherein the base layer is formed of the silicone resin mixed with at least one of alumina powder and silica powder. 
     
     
       5. The circuit protecting element of  claim 1 , wherein at least parts of the insulating substrate bulge out from the base layer. 
     
     
       6. The circuit protecting element of  claim 1 , wherein a blowout section is formed by providing the element with the plurality of trimming grooves. 
     
     
       7. The circuit protecting element of  claim 1 , wherein the base layer is formed of a mixture of diatom earth and silicone resin. 
     
     
       8. The circuit protecting element of  claim 1 , wherein the insulating layer is further comprised of a second insulating layer placed on the first insulating layer. 
     
     
       9. A method of manufacturing a circuit protecting element, the method comprising:
 forming a pair of surface electrodes on both ends of a top face of an insulating substrate; 
 forming a base layer on the top face of the insulating substrate such that at least parts of the surface electrodes can be exposed; 
 forming an element for bridging the pair of surface electrodes on a top face of the base layer, and for electrically connecting with the pair of surface electrodes; 
 irradiating the element with a laser beam so as to form trimming grooves for forming a blowout section; and 
 forming a first insulating layer so as to cover at least the blowout section, 
 wherein the first insulating layer physically contacts the base layer via the trimming grooves, 
 wherein none of the trimming grooves reach the insulating substrate, 
 wherein the element comprises a first element for bridging the pair of surface electrodes and for electrically connecting with the pair of surface electrodes, and a second element for bridging the pair of surface electrodes and for electrically connecting with the pair of surface electrodes, 
 and wherein said forming of the element includes forming the first element by a sputtering method and forming the second element on a top face of the first element by a plating method. 
 
     
     
       10. The manufacturing method of  claim 9 , further comprising:
 after said forming of the first insulating layer, forming a second insulating layer on a top face of the first insulating layer. 
 
     
     
       11. A method of manufacturing a circuit protecting element, the method comprising:
 forming a pair of surface electrodes on both ends of a top face of an insulating substrate; 
 forming a base layer on the top face of the insulating substrate such that at least parts of the surface electrodes can be exposed; 
 forming an element for bridging the pair of surface electrodes on a top face of the base layer, and for electrically connecting with the pair of surface electrodes; 
 irradiating the element with a laser beam so as to form a pair of first trimming grooves for forming a blowout section, and so as to form a plurality of second trimming grooves for adjusting a resistance value; and 
 forming a first insulating layer so as to cover at least the blowout section, 
 wherein the first insulating layer physically contacts the base layer via the first and second trimming grooves, 
 wherein the first and second trimming grooves do not reach the insulating substrate, 
 and wherein the pair of first trimming grooves for forming the blowout section are formed before the plurality of second trimming grooves for adjusting the resistance value are formed. 
 
     
     
       12. The manufacturing method of  claim 11 , wherein a space between the pair of first trimming grooves for forming the blowout section is set to be identical to or smaller than a space between adjacent ones of the plurality of second trimming grooves for adjusting the resistance value, and to be identical to or smaller than a space between each of the first trimming grooves for forming the blowout section and a respective adjacent one of the second trimming grooves for adjusting the resistance value. 
     
     
       13. The manufacturing method of  claim 11 , wherein the pair of first trimming grooves for forming the blowout section are formed only when a resistance value of the element, on which the pair of first trimming grooves for forming the blowout section are not yet formed, falls within a given range. 
     
     
       14. The manufacturing method of  claim 11 , wherein the plurality of second trimming grooves for adjusting the resistance value are formed only when a resistance value of the element with the pair of first trimming grooves for forming the blowout section formed thereon falls within a given range. 
     
     
       15. The manufacturing method of  claim 13 , wherein an open-cut groove is formed on the element when a resistance value of the element, on which the pair of first trimming grooves for forming the blowout section are not yet formed, falls outside the given range. 
     
     
       16. The manufacturing method of  claim 11 , wherein the base layer is formed of a mixture of diatom earth and silicone resin. 
     
     
       17. The manufacturing method of  claim 11 , further comprising:
 after said forming of the first insulating layer, forming a second insulating layer on a top face of the first insulating layer. 
 
     
     
       18. The manufacturing method of  claim 11 , wherein the element can form meanders. 
     
     
       19. The manufacturing method of  claim 9 , wherein the base layer is formed of a mixture of diatom earth and silicone resin. 
     
     
       20. The manufacturing method of  claim 9 , wherein the second element is formed by an electroless plating method. 
     
     
       21. The manufacturing method of  claim 9 , wherein said forming of the first element comprises forming a plurality of first elements while the insulating substrate is heated from the base layer side. 
     
     
       22. The manufacturing method of  claim 9 , wherein a stop-off sheet is pasted to a rear face of the insulating substrate before the second element is formed for preventing plating material from attaching to the rear face. 
     
     
       23. The manufacturing method of  claim 22 , wherein the stop-off sheet is pasted to the rear face by using a temperature of a plating solution.